(1) Field of the Invention
The present invention relates to a projection type display apparatus for displaying an image which forms an optical image in accordance with an image signal with an image display element to be projected to a screen or the like.
(2) Description of the Related Arts
In the case where optical modulation by an image display element is executed in order to minimize the illuminance in an optical system of a conventional projector, there occurs a phenomenon so-called reduction of contrast in which light absorbed by an emission polarization plate which aligns polarization of light fluxes modulated by the image display element is not sufficient and the illuminance on a screen is not lowered.
In addition, there is means for improving contrast by decreasing the minimum illuminance of a projection type display apparatus for displaying an image by photochromatic means which changes the amount of light of the entire screen in accordance with a signal from outside, other than light valves. The signal from outside in this case includes an image signal, a signal obtained by measuring the environments of outside, and a signal intentionally operated by a user. As one of the means, a technique using light shielding means which changes the amount of light shielded in accordance with an image signal in an illumination optical system is disclosed in WO2003-032080, Japanese Patent Application Laid-Open No. 2005-17500, and Japanese Patent Application Laid-Open No. 2005-31103.
In the case where a dynamic range of the projection type display apparatus for displaying an image is further increased, it is necessary to further increase even the amount of light shielded by the light shielding means arranged in the illumination optical system. In order to increase the amount of light shielded by the light shielding means, light shielding areas where illumination light fluxes are light-shielded by a light shielding member included in the light shielding means is increased.
However, if the amount of light shielded is increased, the number of secondary light source images superimposed on an illuminated area of the illumination optical system formed by a lens array is decreased, and thus, illuminance distribution in the illuminated area of the illumination light is likely to be nonuniform. In addition, in the case where the light shielding means rotates (turns) or moves light shielding plates to perform light shielding, changes of the illuminance distribution at the time of movement or rotation of the light shielding plates are likely to be displayed on a screen.